Field of the Invention
The invention relates to a method and a device for the dynamic reservation of HARQ process numbers for a transmission resource especially in the case of LTE.
Discussion of the Background
The number of terminal devices for mobile communication has been increasing worldwide, as has the desire to implement applications with these terminal devices which require a fast transmission rate and have hitherto been limited to classic computer systems. For this reason, existing mobile-radio networks are constantly being expanded. The latest mobile-radio standard for this purpose is LTE (English: Long Term Evolution; German: Langzeitentwicklung), which has been standardized by the 3GPP (English: 3rd Generation Partnership Project; German: Partnerschaftliches Projekt der dritten Generation).
Dependent upon the digital modulation type used, approximately 100 Mbits/s per antenna can be transmitted from the base-station to a mobile-terminal device. In this context, the payload data are transmitted from the base-station to the mobile-terminal device on the PDSCH (English: Physical Downlink Shared Channel; German: geteilter physikalischer Kanal auf der Abwartsstrecke). A different number of frames (German: Rahmen), which are 10 ms long and contain ten subframes (German: Unterrahmen), is provided within the PDSCH dependent upon the bandwidth, whereas each subframe comprises two slots (German: Schlitze). Each subframe lasts 1 ms and contains between 6 and 100 resource blocks (1.4 MHz to 20 MHz). A resource block lasts 1 ms and contains 12 orthogonal carriers which are spaced 15 kHz from one another (special carrier intervals of 7.5 kHz are also possible). A radio resource (English: radio resources), which is also referred to below as a transmission resource, can be described as a two-dimensional time-frequency matrix, which corresponds to a set of OFDM symbols (English: Orthogonal Frequency Division Multiplexing; German: Orthogonales Frequenzmultiplexverfahren) and subcarriers (English: subcarrier). In the case of LTE, the smallest unit for the transmission of data comprises a pair of radio resources with a bandwidth of 180 kHz during a subframe 1 ms long, whereas, in the following description, the term radio resource, or also transmission resource, defines a bandwidth of 180 kHz during a 1 ms-long subframe.
As soon as the base-station transmits payload data to the mobile-terminal device, the latter notifies the mobile-terminal device, inter alia, on which subframe and in which frame the payload data are transmitted. Accordingly, the base-station notifies the mobile-terminal device regarding the location of the transmission resource in the time and frequency domain. This notification takes place on the PDCCH channel (English: Physical Downlink Control Channel; German: physikalischer Kontrollkanal auf der Abwartsstrecke). If very many users of the base-station receive only very small data packets at periodic intervals, a great many messages must be exchanged over the PDCCH. Accordingly, a mismatch occurs between the transmitted payload data by comparison with the transmitted control data, and the overhead increases. In order to counteract this problem, the SPS protocol (English: Semi-Persistent Scheduling; German: Kalb-statische Zeitplanung), the standard underlying the LTE, has been added by the 3GPP. With the use of SPS, the transmission resources can be configured in a semi-persistent manner and are assigned to a mobile-terminal device for a time period which is longer than one subframe. Following this, no further control messages or control data for the assignment of a transmission resource are transmitted on the PDCCH, subject to the exception that the semi-persistent assignment of the transmission resource is cancelled again.
In this context, the period with which the transmission resources are repeated is communicated to the mobile-terminal device, so that the latter can receive the periodically communicated payload data and/or scheduling grants (English: scheduling grants). The overhead between the transmitted payload data and the control data is therefore significantly reduced.
HARQ (English: Hybrid Automatic Repeat Request; German: hybride automatische Wiederholungsanfrage), also referred to as hybrid ARQ processes, are used to determine and correct transmission errors. HARQ is an expanded variant of the ARQ transmission security method, in which the ARQ mechanisms (checksum formation, block acknowledgement, block repetition) are combined with an error-correction coding. For this purpose, various HARQ processes are available at the transmitter end and also at the receiver end, within the MAC layer (English: Medium Access Control Layer; German: mittlere Zugriffskontrollschicht). Altogether, eight different HARQ process numbers (0 to 7) are provided for each receiver at the transmitter end, and also at the receiver end. In order to achieve a valid result, the data packets which are transmitted from the base-station to the mobile-terminal device and processed, for example, in the base-station, using the HARQ process which provides the process number 1, must also be processed in the mobile-terminal device using the HARQ process which provides the process number 1.
Fixed HARQ process numbers are assigned to the transmission resources configured in a semi-persistent manner by SPS. For example, the operator of a base-station can specify that the HARQ process numbers 0 to 3 should be used only for SPS transmission resources. These HARQ process numbers are then no longer available for other transmission resources between the base-station and the corresponding mobile-terminal device. This can lead to the situation that no further HARQ processes are available for the normal transmission resources, so that the data rate for the latter can collapse.
A method and a device which allow HARQ process numbers to be supplied to a common pool after a successful SPS transmission is known from US 2009/0287976 A1. HARQ process numbers which have been supplied to this pool can also be used for normal transmission resources. The disadvantage with US 2009/0287976 A1 is that, with a common pool in which all HARQ process numbers are stored after a successful transmission, it is not guaranteed that the HARQ process number required for the next SPS-configured transmission resource is free and can be used.
A randomly free HARQ process number cannot be used for an SPS-configured transmission resource.